The Ir-5d electrons in most iridate pyrochlores R2Ir2O7 (R = Y, Rare Earth) exhibit a metal-insulator transition accompanied by an ordering of the Ir sublattice. This induces an "all-in all-out" magnetic field on the R moments through the f-d exchange. This well-controlled staggered molecular field is a new parameter allowing to explore the rich physics of rare-earth pyrochlores. It is expected to strongly depend on the single-ion magnetocrystalline anisotropy of the rare-earth and on the interactions between the rare-earth playing a role at a much lower temperature than the Ir ordering. The aim of this proposal is to measure at very low temperature the magnetic diffuse scattering on the D7 spectrometer in order to unveil the ground states of three compounds: (i) Ho2Ir2O7, with an easy-axis anisotropy and ferromagnetic interactions competing with the "all-in all-out" magnetic field, (ii) Yb2Ir2O7, with an easy-plane anisotropy where no signature of any ordered moment was detected, (iii) Gd2Ir2O7, with an isotropic moment which shows the peculiar coexistence of long-range and short-range order at 2 K.